restapi: #868626 - Add "All-Content" Header.

Added header 'All-Content' (values: 'true'/'false') that states whether the entity fetched
should contain all possible information, or only the basic inforamtion (which is most of
the information, but there's still a difference).

The patch maintains backwards compatiblity - information that was returned so far without
"All-Content=true" will still be returned.

This behavior is intended for GET requests.
Create (POST) and Update (PUT) will always return the full entity.

Change-Id: I2b0faf2843ec368fafd5270dc23d711d0710bd48
Bug-Url: http://bugzilla.redhat.com/868626
Signed-off-by: Ori Liel <oliel@redhat.com>